The present invention relates to carbon black for a tire tread rubber, and more particularly, to carbon black which can remarkably lower the heat build-up in a tire tread rubber while keeping the abrasion resistance of the tire tread rubber on a conventional level.
The effect of reinforcing a rubber by carbon black has heretofore been considered to be largely governed by the specific surface area (particle size) and the structure of carbon black. Accordingly, there are known many grades of carbon black differing in these properties.
In compounding carbon black into a rubber component, an appropriate choice is made of the grade of carbon black having characteristics adapted to the application of a rubber composition to be prepared. For example, a hard grade of carbon black, such as N110 or N220, is used in a rubber member requiring a high abrasion resistance, such as a tire tread portion subject to severe running conditions. As the running conditions for tires have recently become more and more severe, however, such a high performance has been required of a tire tread portion so as to satisfy particularly a high abrasion resistance and a low heat build-up at the same time.
In general, it is known that the abrasion resistance of a tire tread portion is enhanced as the specific surface area and structure of carbon black compounded thereinto are increased. However, it is also known that the heat build-up in the tire tread portion is increased in keeping with increases in the specific surface area and structure of carbon black. Thus, the abrasion resistance has an antinomic relation with the heat build-up. Accordingly, it has been considered extremely difficult to simultaneously impart a high abrasion resistance and a low heat build-up to a rubber composition.
With a view to solving such a difficulty, there have been proposed various attempts to use carbon black having specified properties (see, e.g., Japanese Patent Publication No. 53-34149 and Japanese Patent Application Kokai Publication No. 63-112638). Despite such proposals, however, no rubber compositions containing, compounded thereinto, carbon black having such specified properties can simultaneously secure the satisfactory levels of abrasion resistance and heat build-up, in which further improvements has therefore been demanded.
In view of the above, the inventors of the present invention have made investigations on the intraaggregate void volume of carbon black and found that, when carbon black in the form of aggregates having a certain structure level and a relatively small intraaggregate void volume is compounded into a rubber component, the resulting rubber composition has a high abrasion resistance and a low heat build-up. The present invention has been completed based on this finding.